And what does the puppet mesh look like? What are the starch/ stiffness parameters?
To fix the distortion just increase the number of triangles in the mesh. To understand why this works read on.
There are a few things happening here. First, the mesh is seldom precisely lined up with the position of the pins. Second, distortion is applied through the relationship of the pin position to the mesh. When you rotate the parent null the relationship of the pins to the mesh changes. This is just simple geometry. I hope I'm explaining this well. It's much easier to see for yourself if you view your mesh and set the number of triangles to something low like 10.
Take a look at these examples using just 3 pins. First the original with just 10 triangles:
Rotate 45º and the shape is distorted:
Increase Triangles to 200 and the distortion almost disappears:
If you precisely line up your pins on the points of the triangles in your mesh you will get no distortion.
Thank you for this detailed and exemplified response, everything you are saying makes sense, and the examples seem to be exactly what I am dealing with. I tested out this troubleshooting option, but unfortunately, my mesh is still not working. I tried different values of triangles - 200, 350, 370, 600, 900, and even 1500 (the max), and it still warps. My best number was 1024, but that also seems ridiculously high. Could it be because my pin placements are not linear enough? Or there are too many in such a small area? My triangles don't seem to distribute as well as yours. Here are pictures of my mesh:
Thank you for the quick response. I haven't placed any starch points onto the mesh, I likely would on the mid-ankle. I have put some pictures of my mesh in response to Rick below, if you could take a look at them.
Try expanding your mesh. That should solve it. You might have to start over. Generally when I work with Puppet Pin I expand the mesh about 10% if the layer is made up of curves.
I played with mesh expansion a little bit, and it did seem to help. I also scaled the asset up, before importing it, and that seemed to help as well. Things to keep in mind for the future! Thanks for the help, Rick, I really appreciate it.